In qEEG and evoked potential measures, how much of what we see is state-based and thus dependent on issues such as emotional arousal, thought processes, self-monitoring, or directed attention? How much is representative of stable, lasting trait characteristics?
The patient’s emotional and cognitive states are clearly recognized as having significant impact on electrophysiological patterns recorded at the time of an EEG study. Alertness is among the most widely considered state characteristics needing close monitoring during recording, but level of emotional arousal and associated thought patterns are less clearly or consistently measured. How much impact do patients’ short-term emotional and cognitive states have on EEG findings?
The question also arises as to how longer-lasting states, such as periods of several days, weeks, or months, impact EEG patterns. Patients experiencing a time-limited period of intense situational stress, for example, or those who are suffering from mood or anxiety disorders of shorter duration could display different EEG findings than patients with a similar type and severity of symptomatology of much longer, more stable duration. Presumably, patients’ qEEG patterns may also differ significantly from their own when recorded in a different state, short- or longer term. And some do. Several patients in our clinic with repeat studies show very different qEEG topographical and focal findings at various points in treatment.
Yet many other psychiatric patients in our practice have lasting characteristic patterns that remain over the course of several years, unchanging to the course of treatment or shift in symptom presentation. They seem to have consistent signature patterns like an electrophysiological thumbprint. We have found that other aspects of electrophysiology, such as epileptiform activity and evoked potentials, seem to have a similar trend. While some patients have epileptiform activity that appears on only one study out of several repeat studies, others have fixed epileptiform activity in the same region over the course of several years, and yet others have epileptiform activity appearing across studies but shifting in location. Similarly, some patients have a very characteristic P300 wave in response to auditory or visual stimuli over years, while others change in shape, amplitude, and latency. What contributes to the stability of some and to the inconsistency in others?
Researchers and clinicians continue to explore the meaning of various EEG abnormalities, such as epileptiform activity or various types of excess/deficit frequencies in focal or widespread regions. And as we begin to pursue answers in both the lab and the clinic, it is worth discussing how and why some patients, outside of developmental changes, display the same characteristic brain patterns over the course of treatment, regardless of symptom presentation, while others show notable shifts.
- What have you found in your research and/or clinical experiences in terms of repeated EEG or evoked potential studies? What features appear stable and which seem more transient?
- Are stable, signature-like findings associated with any kind of behavioral, cognitive, or emotional characteristics in a particular group of patients?
- What are some difficulties that have arisen as a consequence of state versus trait issues in EEG, and how do we address them as a field?
In a community-based, neuropsychiatric outpatient clinic, we assessed monozygotic twins and their biological mother with standardized clinical interview and self-report questionnaires, qEEG and positron emission tomography (PET). The twins were 30 year-old males, one of whom presented predominantly with obsessive-compulsive disorder, the other who struggled with recurrent major depressive disorder and suicidality. The mother had a history of traumatic stress. While all three had some symptoms related to anxiety, individually their primary concerns were very different.
Neuroimaging supported both state and trait characteristics. EEG findings across all three included epileptiform activity over sensorimotor regions and well-developed auditory EPs compared to poorly-defined visual EPs. PET findings revealed all three had significant asymmetric metabolic uptake in the thalamus, with greater uptake in the left thalamus.
The twins and their mother also each had a unique neurophysiological signature. The twins, but not their mother, had higher alpha amplitudes in left occipital regions. The twin suffering from OCD had absolute power deficits in slow frequencies in right inferior temporal regions as well as deficit beta frequencies in the motor cortex. The twin experiencing severe depression demonstrated excess beta frequencies in the right parahippocampal region. Their mother showed excess beta in superior temporal regions.
Thus it appeared that these individuals seemed to share some stable trait features such as hypometabolism in the right thalamus, while other features such as focal EEG findings may be more reflective of their state.
Do you have case samples, related literature, or observation of state v. trait issues?